feat: add envExists cheatcode to check if a environment variable exis…

…ts (#7744)

crates/cheatcodes/spec/src/vm.rs

@@ -1501,6 +1501,10 @@ interface Vm {
     #[cheatcode(group = Environment)]
     function setEnv(string calldata name, string calldata value) external;
 
+    /// Gets the environment variable `name` and returns true if it exists, else returns false.
+    #[cheatcode(group = Environment)]
+    function envExists(string calldata name) external view returns (bool exists);
+
     /// Gets the environment variable `name` and parses it as `bool`.
     /// Reverts if the variable was not found or could not be parsed.
     #[cheatcode(group = Environment)]

crates/cheatcodes/src/env.rs

@@ -26,6 +26,13 @@ impl Cheatcode for setEnvCall {
     }
 }
 
+impl Cheatcode for envExistsCall {
+    fn apply(&self, _state: &mut Cheatcodes) -> Result {
+        let Self { name } = self;
+        Ok(env::var(name).is_ok().abi_encode())
+    }
+}
+
 impl Cheatcode for envBool_0Call {
     fn apply(&self, _state: &mut Cheatcodes) -> Result {
         let Self { name } = self;

testdata/default/cheats/Env.t.sol

@@ -13,6 +13,14 @@ contract EnvTest is DSTest {
         vm.setEnv(key, val);
     }
 
+    function testEnvExists() public {
+        string memory key = "_foundryCheatcodeEnvExistsTestKey";
+        string memory val = "_foundryCheatcodeEnvExistsTestVal";
+        vm.setEnv(key, val);
+        require(vm.envExists(key), "envExists failed");
+        require(!vm.envExists("nonexistent"), "envExists failed");
+    }
+
     uint256 constant numEnvBoolTests = 2;
 
     function testEnvBool() public {